1. Field of the Invention
The invention relates to latch assemblies and, more particularly, relates to an improved method and apparatus for mounting a latch assembly onto, and disconnecting a latch assembly from, a switch operator.
2. Discussion of the Related Art
Electrical switches, such as pushbuttons or rotary switches used for the control of industrial equipment, are typically mounted on a front panel of a cabinet so that the manipulated portion of the switch (termed the xe2x80x9coperatorxe2x80x9d) projects out from and is accessible at the front of the cabinet.
For a pushbutton switch, a hole may be punched in the cabinet of sufficient diameter to accommodate the pushbutton and a surrounding threaded shaft. The shaft and pushbutton are inserted through the hole, and a threaded retaining nut is placed over the shaft and tightened to securely affix the switch to the panel. The panel is thus sandwiched between the switch body and the retaining nut.
The end of the switch operator protruding inside of the panel is connected or otherwise mounted onto one side of a latch assembly. Various contact blocks, depending on the particular configuration desired, may be bolted or otherwise mounted onto the other side of the latch assembly. The contact blocks are wired to the circuit or circuits that the switch is to control.
To conserve space on the panel and facilitate easy access to the operators by the attending user, several switches are located on the cabinet in close proximity. The spatial arrangement is usually limited by the size of the contact blocks on the back of the cabinet, which typically consume more space than the switch operators. However, with the contact blocks positioned in close proximity to each other, a technician must first remove the necessary contact block before various wiring operations may be performed.
Various approaches have been implemented in the past to enable the connection and disconnection of contact blocks from switch operators. These approaches typically involve mounting the contact block onto a housing having a secondary movable member that can be swiveled, lifted, or otherwise actuated to permit the disconnection of the contact block from the switch operator. However, several disadvantages are associated with these previous devices. First, the implementations can be difficult to use, as their operation is non-intuitive. Specifically, they require the continued actuation of the movable member by the user while removing the assembly from the operator. The user must therefore use two hands to disconnect the contact block from the switch operator, which can be quite difficult given the small amount of space with which to work between the contact blocks that are mounted on the panel. Additionally, once the contact block is disconnected from the operator, the movable member often must be actuated a second time either to permit reconnection of the contact block, and possibly a third time after reconnection to secure the contact block in connection with the operator. Additionally, if the contact blocks are insecurely connected to the switch operators and become dislodged, actuation of the switch operator does not have the desired effect on the controlled circuit. This results in stoppage of the controlled function or, if the switch is controlling, for example, an emergency stop function, more unfortunate results will ensue. Emergency stop (or E-Stop) functions are normally closed contacts that open when the operator is actuated. If the contact block becomes disengaged from the operator, then the controlled function would not stop when the operator is actuated, thereby resulting in malfunction. Additionally, the non-intuitive nature of the device""s operation facilitates misuse by the user, which often leads to breakage of the device.
The need has therefore arisen to provide a latch assembly for connecting a contact block to a switch operator that can be mounted onto a shaft of the operator and subsequently removed with one hand, that prevents the unintentional disengagement of the contact block from the switch operator, and whose use is intuitive to the user.
It is therefore an object of the present invention to provide a latch assembly: 1) that allows a contact block to be easily connected to a switch operator, secured in the connected position, and subsequently disconnected from the operator, that comprises a self-retained locking mechanism that locks automatically upon insertion, thus minimizing the risk that the latch assembly will become unintentionally disengaged from the switch operator; 2) that may be operated with one hand; and 3) whose use is intuitive to the user.
It is a second object of the invention to provide a latch assembly that may be easily actuated in tight spaces to permit the user to perform various wiring operations to an associated contact block.
In accordance with a preferred embodiment of the invention, a latch assembly is provided that comprises a collar mounted onto a housing, and a spring disposed within the housing. The spring is inserted into an arcuate slot in the housing such that one end of the spring is biased against an extending arm of the collar. A contact block may be mounted to the rear face of the housing such that the latch assembly acts as an intermediary between the contact block and the switch operator to which it is mechanically connected. The switch operator includes a stem that passes through the latch assembly and mechanically engages and actuates a switch on the contact block.
The collar, when in a first, locked position, permits the mounting of the latch assembly onto a shaft of the switch. The collar may then be rotated to a second, self-retained, unlocked position, which permits the latch assembly to be removed from the shaft. Once the latch becomes disconnected from the shaft, the spring automatically rotates the collar back to the locked position.
While the latch assembly is being mounted onto the switch in its proper orientation, ensured by a key within the assembly, latch arms on the collar that extend downwardly into the housing are aligned with slots on the shaft of the switch. As the assembly receives the shaft, the latch arms engage the slots until they slide over bottom lips of each slot, thereby forming an interference fit between the latch arms and the slots, and retaining the switch inside the assembly.
Before the latch assembly is removed from the switch, the collar is first rotated to the self-retained, unlocked position. When this occurs, the extending arm of the collar compresses the spring. Additionally, while the collar is rotated, the latch arms slide radially from the slots onto respective smooth surfaces of the shaft. Because the distance between the smooth surfaces is greater than the distance between the two latch arms, the latch arms become deflected radially outward from their normal position when the collar is rotated to the unlocked position. As a result, a finger of one of the latches interferes with a catch disposed within the housing. Although the spring is compressed and provides a force onto the extension arm and towards the collar""s first position, the user may nonetheless let go of the collar as the interference between the finger and the catch prevents the collar from returning to its locked position while the shaft is disposed within the latch assembly. Additionally, when the latch arms are disposed on the respective smooth surfaces adjacent the slots, the latch arms ride axially along the smooth surfaces as the assembly is removed from the shaft. The collar will stay in place without the interference with the finger and the catch due to the frictional forces between the latch arms and the shaft and the collar and housing. However, the interference adds to the insurance that the collar will be retained in its proper orientation.
Once the latch assembly is dismounted from the shaft, the latch arms return to their normal position, thereby becoming disposed radially inward of the catch in the housing and alleviating the interference that was retaining the collar in its unlocked position. The spring then releases, applying a force to the extending arm of the collar and rotating the collar once again to its locked position, where the assembly is again ready to be mounted onto another shaft. Walls in the collar butt against walls in the housing to prevent the over-rotation of the collar in its locked and unlocked positions.
Additionally, in accordance with a preferred embodiment of the invention, the collar has an extending tab that protrudes upwardly away from the contact block. Therefore, to rotate the collar, the user may either rotate the tab by hand, or, because the tab includes accessible grooves, the user may apply a force to the tab using one of many possible tools to rotate the collar. Once the collar is rotated, the user may then pull the latch assembly off of the shaft, thereby returning the collar to its locked position, where the latch assembly may be once again mounted onto a shaft, as previously described.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes ail such modifications.